In recent years, the compression ignition engine industry has come to recognize that common rail fuel systems may have certain advantages over other previously known fuel systems with regard to increasing performance while reducing undesirable emissions. Undesirable emissions include, but are not limited to, NOx, hydrocarbons and particulate matter. Common rail fuel systems typically include a shared reservoir or common rail containing fuel pressurized by a high pressure pump. Individual fuel injectors for each engine cylinder are positioned for direct injection into the respective cylinders and are individually fluidly connected to the common rail via separate branch passages. Originally, common rail fuel systems included some sort of electronically controlled valving system that allowed each fuel injector to be connected to the common rail for an injection event at any desirable engine timing independent of engine crank angle. However, such system were limited as far as injection pressure to the pressure of the fuel in the common rail.
A later innovation in common rail fuel systems is disclosed, for instance, in U.S. Pat. No. 6,675,773 to Mahr et al. This reference teaches the incorporation of a previously known intensifier piston into a common rail fuel injector. Using appropriately controlled valves, this fuel injection system has the ability to inject directly from the rail as in previous common rail systems, but also inject at an elevated or intensified pressure utilizing the intensifier piston. The intensifier piston typically includes a pressure increase via a step piston that includes a large surface area and a small surface area. The large surface is acted upon by rail pressure, and the fuel adjacent the small surface in increased in pressure in proportion to the area ratio between the large surface and small surface. Although fuel systems of the type described in the '773 patent appear to show promise, they are not without problems. For instance, different fuel injectors that appear identical will behave differently because of the multitude of stacked interactions of various components within the fuel system. In addition, these system variations can also change over time. Furthermore, there is always an urge in the industry to seek ever higher injection pressures, which tend to compound all of the other problems associated with fuel injector control and performance variations among apparently identical fuel injectors. Finally, the industry continues to demand ever more versatility, repeatability and reliability from all fuel injection strategies.
The present disclosure is directed to one or more of the problems set forth above.